Phenytoin is the generic name for 5,5-diphenyl-2,4-imidazolidinedione. It also is known as diphenylhydantoin. It is used extensively to treat convulsive disorders such as epilepsy. Because phenytoin is poorly soluble in aqueous mixtures, it cannot be effectively used in injectable solutions, or even in solid preparations for oral use. The compound generally is utilized as a sodium salt, which is readily soluble in water. However, even sodium phenytoin anhydrate rapidly dissociates into phenytoin, which then precipitates from aqueous solutions, thereby making uniform dosing difficult. Moreover, commercial production of sodium phenytoin anhydrate results in complex mixtures of polymorphic forms of the product, and the individual polymorphs exhibit different aqueous solubilities and dissolution rates, thereby further exacerbating dosing irregularities. To date, there has been no single crystal form of any phenytoin sodium capable of analysis by x-ray diffraction.
An object of this invention is to provide a new chemical substance that is a crystalline form of a monohydrate of sodium phenytoin. The new compound can be crystallized into a single crystal form which can readily be analyzed by x-ray diffraction. The sodium phenytoin monohydrate crystal form of this invention is stable for prolonged periods of time, and it exhibits excellent aqueous solubility characteristics, thereby allowing for improved uniformity of dosing. The new chemical compound is readily formulated for both oral and parenteral administration to humans for treatment of epilepsy and other convulsive disorders.